Apparatus for charging fibrous material into a digester



Jan. 18, 1949. J. c. F. c. RICHTER APPARATUS FOR CHARGING FIBROUS MATERIAL INTO A DIGESTER Filed July 30, 1945 Johan Chrislo/fcr fh dn'k 1 Richie/- Patented Jan. 18, 1949 APPARATUS FOR CHARGING FIBROUS MATERIAL INTO A DIGESTER Johan Christofl'er Fredrik Carl Richter, Oslo,

Norway, assignor to Aktiebolaget Kamyr, Karlstad, Sweden, a company of Sweden Original application December 4, 1943, Serial No.

1945, Serial No. 607,694.

Divided and this application July 30,

In Norway October Section 1, Public Law 690, August 8, 194.6 Patent expires October 15, 1962 8 Claims. 1

The present invention relates to an apparatus for charging a fibrous material, such as wood chips, into the liquid-filled space of a digester under pressure, and is a division of my pending prior application Ser. No. 512,978, filed December I have found that for solving the problem of charging fibrous material, such as wood chips, into a liquid which is under pressure, for instance into the space of a digester that is filled with digester liquor, for'the purpose of efiecting a chemical digestion of the fibrous material, it is not possible directly to apply the methods which have proved feasible for efiecting the feeding of fibrous material into a gas or steam under a pressure even as high as 5 to atmospheres, as for instance, into a defibrator, or into the steamfilled space of a digester. In the last mentioned case it is possible to force the material, such as wood chips, into the digester by means of a plunger or a screw, but when it is a matter of introducing the material directly into a liquid which is subjected to a high pressure, such forcing of the material into the body of liquid by means of a plunger or a screw has proved to be quite impracticable, since due to the pressure of the plunger and, in a still higher degree, owing to the pressure of the screw the fibres in the material will become subjected to such high pressures and great deformations that they will become damaged, with the result that the digester liquor directly attacks the cellulosic material itself, which results in an inferior strength and a lower viscosity of the cellulose produced by the digestion, and in additionthe yield thereof ,is reduced. This is particularly the case if, as often happens, the chips to be fed into the digester have been pretreated with steam and possess a high temperature, in which case the chips are very easily damaged.

While it is possible to feed fibrous material into a vessel filled with steam or gas under a high pressure by means of a sluicing device, since in such case the material in the cells or chambers in the sluicing device may drop out of the cells actuated by their own weight, so that the cells are self-emptying, still it is not possible to use this method of sluicing, however, when it is required to charge the material into a liquid under a high pressure, since in such case the material does not drop out of 'the cells at all or only to a very limited extent, and the largest portion of the material will remain in the cells and will be moved out of the digester.

It has also been proposed to pump the chips into the liquid-filled space of the digester by the use of a large quantity of a circulating liquor, for instance a hundred times the weight of the chips, corresponding to a one per cent mixture.

This large quantity of liquor must be pumped into the digester and shall then tear with it the chips, after which the liquor must be drained off through sieves and be returned to the pump in a circuit outside the digester. For effecting such circulation, however, it is necessary to use a high pressure pump having so large passages between its vanes that ordinary wood chips can pass through without risk of clogging it, and therefore, the efficiency of the pump will be low, which fact together with the necessity of utilizing a very large quantity of circulating liquor entails that this manner of charging the material into the digester becomes too uneconomical for practical use, and in addition there are other disadvantages which need not be discussed inthis connection.

The present invention relates to an apparatus by means of which the charging of a fibrous material such as wood chips, into the liquorfllled space of a digester under pressure can be effected in a simple, reliable and efficient manner. The apparatus according to the invention is mainly characterized by the combination of a feeding screw provided in the feeding end of the digester and surrounded by a sieve in a sieve housing provided at the said feeding end of the digester, and a sluicing device for the fibrous material, such as a rotary cell wheel surrounded by a casing, and at least two conduits which connect the sluicing, device with opposite sides of the sieve in the sieve housing and thus form a circulation system through the sluicing device and the sieve housing, a pump being included in one of said conduits in such manner that circulation of liquid may be maintained by means of said pump from the sluicing device to the space occupied by the feeding screw within the sieve and through said sieve into the sieve housing and from the latter back to the sluicing device.

Owing to the fact that according to the present invention the sluicing device is included in a circulation system in which circulation of liquid is maintained, it is ensured that the material sluiced into the system is positively emptied from the cell of the sluicing device and is transferred to the liquid circulating in the circulation system, after which the said liquid carries the material along to the feeding screw. During the introduction of the wood chips into the circulation system Dy-means ofa cell wheel or other sluicing device, the chips are not subjected to pressure or any deformation of a mechanical kind and are therefore'not damaged In the circulation system the same or approximately the same pressure is maintained as in the digester, and it is evident, therefore, that the feeding screw need not exert such great pressure on the chips, that the latter become damaged, the said feeding screw mainly serving to move the chips down along the sieve towards the interior of the diester.

The single figure on the accompanying drawing illustrates by way of example and somewhat schematically a constructional form of an apparatus according to the present invention.

Raw material, such as wood chips, is continuously supplied to the vertical digester I from the chips receptacle 2 which is provided with a vibration device 3 for effecting a uniform supply of chips to. a measuring apparatus 4, for instance in the form of a conveyer screw having a controllable speed, a blade wheel, a shaking apparatus, or some similar well-known apparatus. In the case here selected as an example the digester I is assumed to be under a pressure which is higher than the vaporization pressure of the digester liquor at the digester temperature used, and for this reason the digester must The feeding of be completely filled with liquor. the raw material from the measuring apparatus 4 into the liquor-filled space under pressure in the digester l is effected by means of a sluicing device, which is illustrated in the drawing as comprising a rotating cell wheel 5 which is surrounded by a casing, and which communicates through a conduit 31 with the space 32 within a sieve B in a sieve housing 33 provided at the;

the direction of the arrow, more liquor entering the cell in the position I2, for instance by leakage from the position l3. At said position Hi the chips are emptied from the cell by the circulating liquor which is pumped by the pump 8 from the sieve housing 33 through the conduit 34 and then through the connection 9 to the cell in the position I3, after which the circulating liquor carries the chips along through the conduit 3| to the space 32 inside the sieve 6, where the chips will be fed downwards into the digester by the feeding screw 1, while the liquor is separated through the sieve 6 and then flows through the sieve housing 33 and the conduit 34 back to the pum 8. The chips having been emptied from the cell in the position [3, the cell continues to rotate and carries along liquor which is emptied in the position l4 into a collecting receptacle l6,

-or digester liquor tank, from which the required. quantity of liquor is returned to the circulation chips will in any way influence the operation of the feeding apparatus.

It will also be understood that the feeding of the chips into the pressure space in the digester via the circulation system by the use of the cell wheel 5 does not entail any mechanical treatment or strain whatsoever on the chips. Neither do the chips become damaged while they are conveyed to the digester by the circulating liquor, The feeding screw 1 mainly serves to keep the sieve 6 clean by moving the chips into the digester, and the pressure that said screw exerts on the chips has no bad effect on the state and condition of the chips.

If the liquor is supplied to the suction side of, the pump ill, for instance to the receptacle l6, as indicated at 28a, then the pump [5 will also serve to introduce into the digester, against the digestion pressure therein, the comparatively small quantity of digester liquor which must be continuously supplied to the digester.

There will be no mechanical wear between the cell wheel 5 and its housing, since no such tight fit between these members are required as would necessitate metallic contact between the same.

Any leakage from the pressure space or from the cell at I3 is taken care of either in the form of a complementary filling of the cell at I2 or as an increased sluicing out at H, which simply means that the pump i5 must have a sumcient capactity to be able to pump into the circulation system both the volume of liquor directly sluiced out at l4, and the liquor escaping from the circulation system by leakage, as well as the digester liquor which may be supplied at 280.

Since the cell wheel itself is a quantity meter, the arrangement as a whole functions without any other control than that of the quantity of chips supplied by the measuring apparatus 4 and of the quantity of digester liquor supplied at 28a and pumped into the system by the pump IS.

The invention is not limited to the feeding be-. ing effected at atmospheric pressure, since the operation will be the same whether there is atmospheric pressure or-any other pressure outside the cell wheel.

'As regards the consumption of power, the circulation pump 8 will operate against a pressure of about 0.5 atmospheres.

, size for a production of 100 to 150 tons ,pulp per 24 hours, the liquor circulation effected by'the pump will entail a power consumption of from 15 to 20 H. P. when a quantity of circulating liquor is used that is one hundred times the weight of the chips in the liquor at any given instant, which means that a one per cent mixture of chips and liquor is fed through the conduit 3|.

At [4 a quantity of liquor will be sluiced out that is about 30 per cent larger than the quantity of chips in loose measure. For a plant of a normal size for a production of 100 to 150 tons pulp per 24 hours, about 1500 liters per minute will be sluiced out, which corresponds to a power consumption of about'60 H. P. for the pump l5 operating against a pressure of 8 to 10 atmospheres.

The power consumption necessary for operating the cell wheel 5 and the screw 1 is of the order of 10 H. P.

The entire feeding system for a plant of the I above-mentioned size thus entails a power con- In a plant of a normal with the use of a high pressure pump in the manner previously suggested as mentioned in the introductory part of this specification, would entail a consumption of power of the order of 500 to 1000 H. P. for a plane of the same size.

I claim:

1. In an apparatus for charging a fibrous material into the liquid-filled space of a digester under pressure, the combination of a sieve housing at the feeding end of said digester, a sieve in said sieve housing enclosing a space at the feeding end of said digester, a feeding screw in said sieve-enclosed space, a sluicing device for the fibrous material, at least two conduits connecting said sluicing device with opposite sides of said sieve in said sieve housing and forming a circulation system through said sluicing device and said sieve housing, and a pump connected to one of said conduits so as to efiect circulation of liquid from said sluicing device to said sleeve-enclosed space and through said sieve into said sieve housing and from the latter back to said sluicing device.

2. In an apparatus for charging a fibrous material into the liquid-filled space of a digester under pressure, the combination of a sieve housing at the feeding end of said digester, a sieve in said sieve housing enclosing a space at the feeding end of said digester, a feeding screw in said sieve-enclosed space, a sluicing device for the fibrous material comprising a rotary cell wheel and a casing surrounding said cell wheel, at least two conduits connecting said sluicing device with opposite sides of said sieve in said sieve housing and forming a circulation system through said sluicing device and said sieve housing, and a pump connected to one of said conduits so as to effect circulation of liquid from said sluicing device to said sieve-enclosed space and through said sieve into said sieve housing and from the latter back to said sluicing device.

3. In an apparatus for charging a fibrous material into the liquid-filled space of a digester under pressure, the combination of a sieve housing at the feeding end'of said digester, a sieve in said sieve housing enclosing a space at the feeding end of said digester, a feeding screw in said sieveenclosed space, a sluicing device for the fibrous material, at least two conduits connecting said sluicing device with opposite sides of said sieve in said sieve housing and forming a circulation system through said sluicing device and said sieve housing, a pump connected to one of said conduits so as to effect circulation of liquid from said sluicing device to said sieve-enclosed space and through said sieve into said sieve housing and from the latter back to said sluicing device, a second pump, the pressure side of said second pump being'connected to the said circulation system, and the suction side of said second pump being connected to said sluicing device so as to return to the circulation system liquid escaping therefrom through said sluicing device.

4. An apparatus as defined in claim 3, wherein a collecting receptacle is connected between the sluicing device and the suction side of the second pump.

5. An apparatus as defined in claim 3, wherein a supply conduit for digester liquor is connected to the suction side of the second pump.

6. In an apparatus for charging a fibrous material into the liquid-filled space 0! a digester under pressure, the combination of a sieve housing at the feeding end of said digester, a, sieve in said sieve housing enclosing a "space at the feeding end of said digester and separating said space from the interior of said sieve housing, a feeding screw in said sieve-enclosed space, a sluicing device for the fibrous material, at least two conduits connecting said sluicing device with opposite sides of said sieve in said sieve housing and forming a closed liquid-filled circulation system through said sluicing device and said sieve housing, and a pump connected to one of said conduits so as to eifect circulation of liquid from said sluicing device to said sieve-enclosed space and through said sieve into said sieve housing and from the latter back to said sluicing device.

7. In an apparatus for charging a fibrous material into the liquid-filled space of a digester under pressure, the combination of a-sieve housing at the feeding end of said digester, a sieve in said sieve housing enclosing a space at the feeding end of said digester and separating said space from the interior of said sieve housing, a feeding screw in said sieve-enclosed space, a sluicing device for the fibrous material comprising a rotary cell wheel and a casing surrounding said cell wheel, at least two conduits connecting said sluicing device with opposite sides of said sieve in said sieve housing and forming a closed liquid-filled circulation system through said sluicing device and said sieve housing, and a pump connected to one of said conduits so as to effect circulation of liquid from said sluicing device to said sieve-enclosed space and through said sieve into said sieve housing and from the latter back to said sluicing device.

8. In an apparatus for charging a fibrous material into the liquid-filled space of a digester under pressure, the combination of a sieve housing at the feeding end of said digester, a sieve in said sieve housing enclosing a space at the feeding end of said digester and separating said space from the interior of said sieve housing, a feeding screw in said sieve-enclosed space, a sluicing device for the fibrous material, at least two conduits connecting said sluicing device with opposite sides of said sieve in said sieve housing and forming a closed liquid-filled circulation system through said sluicing device and said sieve housing, a pump connected to one of said conduits so as to eflect-circulation of liquid from said sluicing device to said sieve-enclosed space and through said sieve into said sieve housing and from the latter back to said sluicing device, a second pump, the pressure side of said second pump being connected to the said circulation system, and the suction side of said second pump being connected to said sluicing device so as to return to the circulation system liquid escaping therefrom through said sluicing device.

JOHAN CmISTOFEER FREDRIK CARL RICHTER.

REFERENCES CITED The following references are of record in th file of this patent:

UNITED STATES PATENTS Number Name Date 1,020,743 Buriingham et 8.]. Mar. 19, 1912 1,564,980 Singer Dec. 8, 1925 1,601,497 Greene Sept. 28, 1926 1,828,488 Carmichael Oct. 20, 1921 2,181,404 Koppitz et a1. NOV. 28, 1939 

